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This article introduces you what is the EMC VMAX RAID implementation mechanism, the content is very detailed, interested friends can use for reference, I hope it can be helpful to you.

Today we're going to talk about Symmetrix VMAX's RAID composition. The RAID composition method of Symmetrix is very strange, and there is very little information on the Internet, because the configuration of VMAX is done by EMC professionals, and the configuration file is still a BIN file, users only need to tell CE (it seems to be so, referring to the certification engineer? CE generates a BIN file based on demand, and then distributes it to each engine This makes many people do not understand how VMAX presents LUN to the host.

Last weekend, in order to figure out this problem, I spent two days (I didn't do the after-sales of symmetrix, so I'm not sure? ) the research has basically made these problems almost clear.

First of all, it starts with my doubts. When I was learning VMAX, the VMAX material clearly wrote that in the open system environment, VMAX does not support RAID 10, only RAID 1, 5, 5, 6. RAID 10 is only supported in mainframe environments.

I didn't understand very well at first. Everyone knows that the performance of RAID 10 is much better than that of RAID 1. What is the reason why VMAX does not need RAID 10? EMC must have other methods of disk striping. I asked a friend of EMC, and he didn't understand (he didn't do high-end work). Asked others, others do not believe that VMAX high-end devices do not support RAID 10 (open environment)?

So I looked through EMC's materials and forums and finally understood why VMAX didn't need RAID 10. I was also surprised by the disk organization of VMAX. It turns out that VMAX does not do RAID based on physical disks, so does VMAX also use block virtualization technology similar to RAID 2.0?

First of all, let's take a look at the differences in terms:

-EMC terms often used are hyper-volume, slice, split, device, or volume. Industry term is LUN- Logical Unit

Then let's brag about why I imagine symmetrix divides LUN in this way.

In the beginning, Symmetrix only supported RAID 1. At that time, Enginuity (this is Symmetrix's OS) was also estimated to be a 32-bit system or less, so each LUN would not be too large or need to be too large. Therefore, Symmetrix buys several watermelon knives of different sizes from Xiaobian, and cuts each watermelon, oh, each hard disk into pieces of different sizes to provide to the host computer.

Generally speaking, in order to facilitate management, the hard disk is cut into blocks of the same size, and the latest version supports cutting a hard disk into 1024 pieces. These blocks EMC have a special name, called hyper volume, or hyper for short. These hyper volume can be mapped directly to the host, and this is the simplest LUN (unprotected). However, if you need to do RAID 1 protection, you need to select two hyper, mirror each other, and then map it to the host. Later, with the development of RAID technology, EMC supports RAID PARITY (somewhat similar to RAID 3, that is, all parity data is stored on a hyper). This technology is not widely used because the hyper of parity will become a bottleneck. Later, EMC began to support RAID 5 and finally RAID 6. If you want to do RAID 5 and RAID 6, you need to select more hyper to form a hyper volume with the attribute of RAID 5 and 6, and then map it to the host for use.

Note that Symmetrix is based on hyper, a CK similar to HW RAID 2.0, to do RAID. In other words, Symmetrix does not do RAID based on physical disks. The original summary of the editor is that RAID based on physical disk is RAID 1.0, and RAID based on virtual disk is RAID 2.0 may be wrong. Does Symmetrix also use RAID 2.0? This question confuses me. Let's put it aside for a while and come back to this question later.

Let's take a look at how a LUN chooses hyper. Let's look at it from a specific example

We can see that it is not possible to specify which hyper to use to make up RAID 5, it should be chosen by the system itself according to certain rules. Moreover, VMAX has the concept of hot spare, so the refactoring time should be the same as traditional RAID, because hot spare will become the bottleneck of refactoring. Unlike RAID 2.0, only hot spare space is needed, not hot spare. All disks can participate in refactoring.

Because the size of hyper is not too large, the maximum size of hyper supported by the latest version of VMAX is 256G. What if more LUN is supported? Let's take a look at the partition process of Symmetrix.

First, in the first step, Symmetrix divides the disk into hyper. Here, for example, each disk is split into eight hyper of the same size.

After the segmentation is completed, multiple hyper are selected to form a meta volume in series or stripe.

This meta volume consists of up to 256 hyper, and the maximum LUN that supports 60TB is presented to the host.

This time, it is clear that Symmetrix does not need to support RAID 10 at all. With meta volume, a LUN can span hundreds of hard drives, so the performance should be much better than the traditional RAID.

Is this what we call RAID 2.0? let's first look at the same place:

1. RAID is done based on disk slices, not physical disks.

2. A LUN can span hundreds of disks, and its performance is much better than that of the traditional RAID 1.0.

But in fact, there is a big difference between them:

Symmetrix still uses the traditional hot spare mode, while RAID 2.0 only needs hot spare space, so Symmetrix does not have the function of fast reconfiguration.

I still admire Symmetrix very much. A long time ago, I used this method to solve the problem of supporting large LUN and solving the performance problem. No wonder Symmetrix's FAST was launched relatively late.

Therefore, today, I revised my previous definition of RAID 2.0: the RAID implementation of RAID based on disk slices and using hot spare space instead of physical hot spare is RAID 2.0.

On what the EMC VMAX RAID implementation mechanism is shared here, I hope that the above content can be of some help to you, can learn more knowledge. If you think the article is good, you can share it for more people to see.

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